This invention relates to the production of compounds containing fluorine-substituted carbon atoms, and more particularly to the production of hydrofluoro compounds containing multiple carbon atoms and/or both carbon and sulfur atoms.
Multicarbon compounds and carbon-sulfur compounds which contain hydrogen and fluorine but no chlorine, have recently been the subject of renewed interest as environmentally desirable compounds for use as solvents, blowing agents and refrigerants. Among these compounds are certain hydrofluorocarbons (i.e., compounds containing only carbon, hydrogen and fluorine) which have typically been produced using catalytic processes for hydrogenolysis and/or hydrogenation of saturated or unsaturated compounds containing both chlorine and fluorine. Certain supported precious metal catalysts are among those considered particularly suited for catalyzing the reactions. British Patent Specification No. 1,578,933 uses a process for the manufacture of CF3CH2F or CHF2CHF2 by the hydrogenolysis of an appropriate haloethane (e.g., CF3CCl2F) over a hydrogenation catalyst such as palladium supported on carbon or alumina. Conventional hydrogenolysis of this type can be used to convert CF3CCl2F to a product mixture including CF3CHClF and CF3CH3 in addition to tetrafluoroethane.
Precious metal catalysts such as palladium are expensive and can deactivate during the course of catalyzed reactions. Replacement and/or regeneration of such catalysts can thus add to the cost of the catalyzed reaction. Also, the use of chlorine-containing reactants such as CF3CCl2F and the production of chlorine-containing products such as CF3CHClF can present handling and disposal concerns.
Iodine or hydrogen iodide have been used in conjunction with the reaction of selected fluorine-containing compounds. For example, U.S. Pat. No. 2,844,636 discloses a process for the manufacture of 1,1,2,3,4,4-hexafluorobutane by reacting perfluoro-cyclobutene with hydrogen, using elemental iodine as a catalyst. In this process not only is there hydrogen addition at the double bond, but also cleavage and hydrogenation at the xe2x80x94CF2xe2x80x94CF2xe2x80x94 single bond to give the substituted normal butane. U.S. Pat. No. 5,097,082 discloses a process for producing saturated halohydro-carbons containing fluorine which comprises the step of reacting certain saturated or olefinic compounds at an elevated temperature with hydrogen in the presence of at least one material selected from the group consisting of iodine and hydrogen iodide, or with hydrogen iodide.
A process is provided in accordance with this invention for producing a compound of the formula RCFZH wherein R is selected from the group consisting of SF5, CF2SF5 and RfCF2Y, Rf is a perfluoroalkylene group containing from 1 to about 12 carbon atoms and optionally containing one or more ether oxygen atoms, Y is selected from H, F, and SF5 and Z is selected from CF2CF3, CF3 and F, by reaction of an iodide compound of the formula Rxe2x80x2CFZI with hydrogen at an elevated temperature, wherein wherein Rxe2x80x2 is selected from the group consisting of SF5, CF2SF5 and RfCF2X and X is selected from H, F, SF5, and I, provided that when Y is F, X is F, when Y is SF5, X is SF5 and when Y is H, X is H or I.
This invention provides a process for producing monohydro and dihydro compounds from corresponding monoiodo and diiodo compounds. The monoiodo and diiodo reactants of this invention include compounds with multiple adjacent carbons (i.e., Cxe2x80x94C bonds) and/or carbon adjacent to sulfur (i.e., Cxe2x80x94S bonds). The monoiodo and diiodo reactants are reacted in accordance this invention essentially without cleavage of these carbon-carbon and carbon-sulfur bonds. The iodide compound reactants of this invention contain an iodine which is either on a difluoro-substituted carbon (i.e., Z is F) or on a monofluoro-substituted carbon adjacent to a CF3 or C2F5 group (i.e., Z is CF3 or CF2CF3). The diiodo compounds all contain at least one iodine which is on a difluoro-substituted carbon. Preferably Z is F, especially when Rxe2x80x2 is RfCF2X.
The monoiodo and diiodo compounds which are reacted in accordance with this invention include (where Rxe2x80x2 is RfCF2X and X is H, F or I) any perfluoroalkyl iodide, perfluoroalkyl diiodide or xcfx89-H-perfluoroalkyl iodide containing from 3 to about 14 carbon atoms and optionally containing one or more ether oxygen atoms. The perfluoroalkylene group, Rf, may be branched or unbranched. Examples of perfluoroalkylene groups which do not contain ether oxygens include for example, xe2x80x94CF2xe2x80x94, xe2x80x94CF2CF2xe2x80x94, xe2x80x94CF2C(CF3)Fxe2x80x94, xe2x80x94CF2CF2CF2xe2x80x94, xe2x80x94CF2C(CF3)2xe2x80x94 and xe2x80x94CF2CF2CF2CF2xe2x80x94. Examples of perfluoroalkylene groups which contain ether oxygens include for example, xe2x80x94CF2OCF2xe2x80x94, xe2x80x94CF2CF2OCF2xe2x80x94, xe2x80x94CF2OCF2OCF2xe2x80x94, xe2x80x94CF2OCF2CF2OCF2xe2x80x94, xe2x80x94CF2CF2OCF(CF3)CF2OCF2xe2x80x94, and xe2x80x94CF2OCF2CF(CF3)OCF2CF2OCF(CF3)CF2OCF2xe2x80x94.
Preferred iodides include mono- and diiodides of the structures CF3RfCF2I and ICF2RfCF2I, where Rf is C1 to C10 perfluoroalkylene, branched or unbranched, and optionally containing one or more ether linkages. Most preferred are iodides of the linear structures F(CF2)nI and I(CF2)nI where n is an integer from 3 to 12. Examples include I(CF2)4I, I(CF2)6I, F(CF2)4I, F(CF2)6I, and F(CF2)8I.
Perfluoroalkyl iodides may be prepared by the addition of either trifluoroiodomethane or pentafluoroiodoethane to tetrafluoroethylene as disclosed by R. N. Haszeldine, J. Chem. Soc., pp. 3761-3768 (1953). Perfluoroalkyl diiodides containing an even number of carbon atoms may be prepared by the addition of 1,2-diodoperfluoroethane to tetrafluoroethylene as disclosed in Houben-Weyl, xe2x80x9cMethoden Der Organische Chemiexe2x80x9d Band V/4, pp. 653-655 (1960). In a similar manner perfluoroalkyl diiodides containing an odd number of carbon atoms may be prepared by the addition of 1,3-diodoperfluoropropane to tetrafluoroethylene. xcfx89-H-perfluoroalkyl iodides may be prepared by the reaction of an xcfx89-H-perfluoroalkyl acid chloride with potassium iodide as disclosed by C. G. Krespan, J. Org. Chem., Vol. 23, pp. 2016-2017 (1958). Perfluoroalkyl iodides containing C3 to C14 carbon atoms and optionally containing one or more ether oxygens may be prepared as disclosed in U.S. Pat. No. 4,275,226, which is hereby incorporated herein in its entirety by reference (see in particular col. 2, lines 46-65).
The monoiodo compounds which are reacted in accordance with this invention also include carbon-sulfur compounds having a pentafluoro sulfur group. Examples include SF5CF2I and SF5CFICF3 (i.e., Rxe2x80x2 is SF5) and SF5CF2CF2I (i.e., Rxe2x80x2 is CF2SF5 and Z is F). SF5CF2I has been prepared by reaction of the silver salt of SF5CF2CO2H with iodine as disclosed by Bekker, et al. in IZV. Akad. Nauk SSSR, Ser. Khim., pp. 2738-2741 (1970). SF5CFICF3 has been prepared by reaction of SF5CFxe2x95x90CF2 with a mixture of iodine and IF5 as reported by Gard and Woolf in J. Fluorine Chem., Vol. 1, pp. 487-492 (1971/2). Longer chain SF5-terminated reactants can generally be prepared in a manner analogous to CF3-terminated compounds. SF5-substituted iodofluoroalkanes containing an even number of carbon atoms (SF5(CF2CF2)nI, where n is an integer from 1 to about 6) may be prepared by reacting S2F10 with CF2ICF2I or with I2 and tetrafluoroethylene as disclosed by Hutchinson in J. Fluorine Chem., Vol. 3, pp. 429-432 (1973/4).
The hydrogenolysis reaction of this invention may advantageously be accomplished in the absence of hydrogenation catalysts. The term xe2x80x9chydrogenation catalystsxe2x80x9d is used herein in the ordinary sense, to signify conventional metal-based hydrogenation catalysts which are in themselves known. Examples of hydrogenation catalysts include nickel or other metals of Group VIII of the Periodic Table (in catalytic form) or oxides or salts thereof. (In use, a compound of such a metal is reduced at least in part to the metal.) In particular, the reaction of this invention may be accomplished in the absence of palladium hydrogenation catalysts. Preferably, the reaction is accomplished in the absence of any supported metal catalysts.
Substantial amounts of iodine are generally produced during the reaction. The iodine recovered from the reaction of hydrogen with the additional monoiodoperfluoroalkanes or diiodoperfluoroalkanes may be recycled by using it to prepare monoiodoperfluoroalkanes or diiodoperfluoroalkanes (e.g., by reacting it with tetrafluoroethylene). xcex1,xcfx89-diiodoperfluoroalkanes may be prepared by the reaction of tetrafluoroethylene with iodine as disclosed by Tortelli et al., J. Fluorine Chem., Vol. 47, pp. 199-217 (1990). Monoiodoperfluoroalkanes may be prepared by reaction of tetrafluoroethylene with iodine in the presence of IF5 and SbF5 as disclosed in U.S. Pat. No. 3,132,185. The iodine produced during the hydrogenolysis may also be used to form potassium iodide. The conversion of iodine to potassium iodide is a well known reaction (see, e.g., CA 111 (24): 216717x). The potassium iodide can then be used to prepare additional amounts of the various mono- and diiodine reactants (i.e., additional iodide compound reactants). For example, KI may be reacted with a xcfx89-H-perfluoroalkyl acid chloride as indicated above to provide a xcfx89-H-perfluoroalkyl iodide.
Substantial amounts of HI may be produced, particularly where excess hydrogen is used during the reaction. The HI can also be used to make I2 (by oxidation) or KI (by neutralization).
Free iodine may be added to the reaction, and may be useful to moderate exothermic reactions at the start of the hydrogenolysis. However, the presence of free iodine is not considered essential for the hydrogenolysis and the reaction may be accomplished without addition of supplemental iodine.
The reaction is performed at an elevated temperature. The reaction temperature should generally be from about 200xc2x0 C. to about 500xc2x0 C. The temperature is preferably about 400xc2x0 C. or less to minimize corrosion, energy requirements, and side reactions (e.g., carbon-carbon bond cleavage). A preferred range is 250xc2x0 C. to 350xc2x0 C. Hydrogenation of diiodo compounds at lower temperatures (e.g., about 200-225xc2x0 C.) typically results in formation of significant amounts of monoiodo compound, which can then be further hydrogenated (by recycle or otherwise) to form the desired dihydro compound.
Typically, the ratio of hydrogen to the iodide compound reactant is within the range of about 10:1 to 1:10. It is preferred that hydrogen be present in no more than stoichiometric amounts. The mole ratio of hydrogen (i.e., H2) to monoiodo compounds is preferably from about 1:2 to about 1:4, and is more preferably about one mole of hydrogen for each two moles of such compounds. The mole ratio of hydrogen to diiodo compounds is preferably from about 1:1 to about 1:2, and is more preferably about 1:1. The hydrogen can be fed either in the pure state or diluted with an inert gas, e.g., nitrogen, helium, or argon. A particular advantage of using no excess hydrogen is that essentially all of the hydrogen may be used for hydrogenolysis; and that there is consequently an absence or near absence of hydrogen and hydrogen iodide in the resulting product. This facilitates the isolation and purification of the hydrogenolysis product. Iodide compounds remaining in the product mixture may be recycled.
The reaction may be operated either in a batch or continuous mode at pressures of from about 10 kPa to about 20xc3x97103 kPa with 101 kPa to about 7xc3x97103 kPa being preferred.
The products of the reaction can be separated and purified by conventional means such as fractional distillation. The products are useful as stable, nonflammable solvents (see, e.g., U.S. Pat. No. 4,243,770), refrigerants, propellants, and cleaning and drying agents.